1. Field of the Invention
The invention concerns an assembly for analyzing a light pattern caused by refraction and reflection at a precious stone, comprising a light source for illuminating the precious stone, a holding device for holding the precious stone, a diffusing screen for imaging the light pattern (in particular, a flat diffusing screen), and a camera for recording the light pattern imaged on the diffusing screen. The invention further concerns a method of analyzing a light pattern caused by refraction and reflection at a precious stone by means of the assembly according to the invention.
2. Description of Related Art
An assembly having the specified components is known, for example, from U.S. Pat. No. 5,828,405. A disadvantage with that assembly in the state of the art is that illumination of the diamond to be investigated is effected by way of an opening in the diffusing screen. The result of this is that the part of the light pattern which would be imaged in the region of that opening on the diffusing screen is lost. In addition, only a small part of the diamond can be illuminated with the illumination arrangement disclosed in U.S. Pat. No. 5,828,405. In that way, also there is a loss of information about the diamond.
Also finally there is the further disadvantage that, by virtue of the geometry of the illumination arrangement, it is necessary for the camera for recording the light pattern imaged on the diffusing screen to be arranged at an angle relative to the screen and, on the other hand, to be positioned relatively close to the diffusing screen. The latter requires the use of an extreme fisheye objective. Overall, the arrangement of the camera in relation to the diffusing screen in U.S. Pat. No. 5,828,405 results in severe perspective distortions of the recorded light pattern. Theoretically, it would admittedly be possible to increase the distance of the camera relative to the diffusing screen so that the camera is disposed, for example, at the height of the precious stone or even behind the precious stone, but then the free view onto the diffusing screen would be restricted by parts of the illumination arrangement or the precious stone itself, which again would lead to information loss.
For the sake of completeness, however, it should also be noted that the aim in U.S. Pat. No. 5,828,405 is to record a characteristic “fingerprint” of a precious stone and to compare it to a fingerprint stored in a database in order to be able to identify the precious stone in the event of theft. As long as the image of the precious stone is always recorded with the same apparatus, information losses and perspective distortions do not play any part.